Comment by bokonist

I have wondered if the 5 hours of heavy coding maximum is psychological or physiological. Does productivity drop because your mind rebels against itself? Prolonged mental focus is an unnatural thing to do in the scheme of evolution. There might be some mental mechanism that automatically triggers feelings of despondency in order to make you do something else. Alternatively, hitting the wall might be an actual physical problem - the brain might be overheating, or have some build of chemicals, or something, that requires a recovery time.